Antennas of radar sensors, which are provided for use in motor vehicles, are often designed as patch antennas on an RF substrate. This allows a cost-effective construction of the radar sensor. By using array antennas, the desired directional characteristic of the radar sensor in azimuth and/or elevation may be achieved without a radar lens being required. Separate antennas are often used for emitting the radar signal and for receiving the reflected signal. The desired directional characteristic of the transmitting antenna in azimuth may be achieved by supplying the multiple adjacent antenna elements on the substrate with in-phase microwave power. A radar lobe is then obtained by interference, whose main direction of emission is oriented at a right angle to the plane of the substrate and which covers an azimuth angle range of approximately −45° to approximately +45°. On the receiving side multiple adjacent antenna elements or patches are also used, which, however, belong to different receiving channels, so that the azimuth angle of the object may be inferred using the phase differences between the signals received by the different antenna elements.
In particular, the present invention concerns a radar sensor system for motor vehicles, which allows the cross traffic to be monitored, for example, in an RCA system (Rear Cross Alert), which supports the driver when backing up from or parking in a parking space by warning of vehicles approaching on a road or a parking lane perpendicular to the longitudinal direction of the vehicle. In this case, the radar sensor system must be capable of locating objects situated at a small distance from one's own vehicle in the longitudinal direction of the vehicle, but are at large azimuth angles to the right or left from one's own vehicle.